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Nano-silicon carbide (nSiC) particle-reinforced aluminium (Al) 6061 alloy matrix composites were fabricated by high-energy ball milling, hot-pressing (HP), and hot-forging (HF). The composite powders were degassed and the composites were synthesised under air and/or vacuum. Mechanical properties of the obtained composite materials were evaluated using various tests, including indentation, compression, four-point bending, and tensile tests as well as by microstructural observations. Different amounts of nSiC were added and the mechanical properties of the obtained composite materials were measured and discussed. The microstructures of the composites depended on the nSiC content and synthesis conditions. The Vickers hardness and tensile strength values of the nSiC reinforced Al 6061 composites were approximately three times higher than that of a pure Al 6061 alloy bulk. The results demonstrated that the small amount of nSiC particles functioned as efficient reinforcement material in the Al 6061 alloy matrix composite material and that the strength and ductility of the composite material can be controlled by adjusting the processing parameters and nSiC content.

Fe–Co alloys are attracting attention as magnetostrictive materials for energy harvesting and sensor applications. This work investigated the magnetostriction characteristics and crystal structure of additive-manufactured Fe–Co alloys using directed energy deposition. The additive-manufactured Fe–Co parts tended to exhibit better magnetostrictive performance than the hot-rolled Fe–Co alloy. The anisotropy energy ΔK1 for the Fe–Co bulk, prepared under a power of 300 W (referred to as bulk−300 W), was larger than for the rolled sample. For the bulk−300 W sample in a particular plane, the piezomagnetic constant d was large, irrespective of the direction of the magnetic field. Elongated voids that formed during additive manufacturing changed the magnetostrictive behavior in a direction perpendicular to these voids. Magnetic property measurements showed that the coercivity decreased. Since sensors should be highly responsive, Fe–Co three-dimensional parts produced via additive manufacturing can be applied as force sensors.

In this study a continuous wave Ytterbium-doped Yttrium Aluminum Garnet (Yb: YAG) disk laser has been used for welding of AlMg3 casted alloy. A high-speed imaging camera has been employed to record hot vapor plume features during the process. The purpose was to identify a mechanism of pores detection in real-time based on correlations between metallographic analyses and area/intensity of the hot vapor in various locations of the samples. The pores formation and especially the position of these pores had to be kept under control in order to weld thick samples. Based on the characterization of the hot vapor, it has been found that the increase of the vapor area that exceeded a threshold value (18.5 ± 1 mm2) was a sign of pores formation within the weld seam. For identification of the pores’ locations during welding, the monitored element was the hot vapor intensity. The hot vapor core spots having a grayscale level reaching 255 was associated with the formation of a local pore. These findings have been devised based on correlation between pores placement in welds cross-section microscopy images and the hot vapor plume features in those respective positions.

Powder additive pulsed Nd:YAG laser (wavelength 1064 nm), with the aim of preparing AM of such material. The influence of oxygen content in the initial silicon powders on the continuous tracks morphology was investigated. It was found that the initial oxygen content of the processed powders must be lower than 0.1 wt% to produce a smooth silicon melted track. This result is explained as due to the formation of gaseous manufacturing (AM) of materials is affected by the oxygen present in the raw material, especially if they possess a native oxide. The latter influences the properties of the laser molten track. We carried out a study on the interactions between silicon fine powder (

Laser produced plasma of carbon nanotube reinforced AlMg5 metal matrix nanocomposites (AlMg5–CNT) is investigated by optical emission spectroscopy which dominantly consists of neutral aluminum (Al I) and magnesium (Mg I) atomic species. The blue-green ( B 2 Σ − X 2 Σ ) band system of AlO and green (1Σ → 1Σ) system of MgO are observed in the optical emission spectra of AlMg5–CNT plasma recorded without Ar shielding gas due to oxidation of Al I and Mg I species in air. The AlO blue-green ( B 2 Σ − X 2 Σ ) band system is also observed with Ar shielding gas in the optical emission spectra of plasma of AlMg5–CNT having oxidized grain boundaries which is irradiated by one or more laser pulses prior to plasma creation. The oxidation of grain boundaries in AlMg5–CNT is found to be nullified as the concentration of CNT reinforcement increases. Furthermore, the intensity ratio (IMgI/IAlI) of Mg I to Al I emission is found to be more for pristine AlMg5–CNT than that for AlMg5–CNT which is shot by one laser pulse prior to plasma creation, indicating more depletion of magnesium relative to aluminum.

Synthesis process of graphene nano-flakes produced in radio-frequency inductively coupled plasma system by axially injecting CH4 into Ar–H2 plasma is investigated at different process conditions such as plate power, pressure and CH4 flow rate. Optical emission characteristics of Ar, Ar–H2, Ar–H2–CH4 and Ar–H2–C2H2 plasmas are sequentially studied to understand different dissociation channels of CH4. Graphene nano-flakes are formed by condensation of C2 species which are generated owing to CH4 decomposition caused by electron impact, dehydrogenation and energy transfer from excited state Ar atoms to C2H2 and/or C2H produced during dissociation. Maximum production rate achieved is ~ 10 g/h at plate power of 22 kW, pressure of 70 kPa and CH4 flow rate of 1.5 slpm at which intensity ratio of D and G band of Raman spectrum is 0.25 in spite of having contribution from edges of nano-flakes to D band intensity indicating good quality. Effect of decrease in cooling rate at the location of nucleation at higher CH4 flow rates ≥ 2 slpm increases average number of graphene layers (#L) which is however reduced with increase in plate power i.e. from #L of 22 to 13 with increase in plate power from 15 to 22 kW at pressure of 70 kPa and CH4 flow rate of 2 slpm.

Additive manufacturing (AM) of brittle materials remains challenging, as they are prone to cracking due to the steep thermal gradients present during melting and cooling after laser exposition. Silicon is an ideal brittle material for study since most of the physical properties of single-element materials can be found in the literature and high-purity silicon powders are readily available. Direct laser melting (DLM) of silicon powder was performed to establish the conditions under which cracks occur and to understand how the solidification front impacts the final microstructure. Through careful control of process conditions, paying special attention to thermal gradients and the growth velocity, epitaxial pillars free of cracks could be grown to a length of several millimeters.

Near net shaped metal matrix composites were fabricated using high energy cube milling and hot pressing process. Cube milling was up to six times faster than commercially available planetary ball mill in dispersing up to 1 vol.% of Al 2 O 3 nanoparticles in AlMg5 alloy. Combined yield strength of 530 MPa and elongation at rupture of 4% exceed the values of commercially available wrought 5xxx series alloys. Thorough microstructure characterisation of composites revealed bimodal grain structure with an increasing content of finer grains and high angle grain boundaries with higher reinforcement content. The main contributing strengthening mechanisms for achieving high strength were solid solution strengthening, Orowan strengthening and grain boundary strengthening. Coarse grained regions in the bimodal structure, together with low angle grain boundaries were assumed to be the main source of retained ductility.

Graphene oxide (GO) powder was dispersed in an AlMg5 matrix using high energy ball milling. The obtained blend was then completely densified by hot pressing. No further hardening processing step was performed. Nevertheless, only 1 vol% of GO in the Aluminum alloy matrix leads to a significant improvement of the mechanical resistance. The ultimate tensile strength (540 MPa) and the macro hardness (166 HV) are increased by a factor of 2 compared to the same AlMg5 alloy without nanoparticulate material and compacted under the same conditions. The bending strength is even increased by a factor of 4 reaching a value over 800 MPa. The GO powder can be applied as a mechanical reinforcement to other scenarios such as polymer and ceramic systems.

Laser Metal Deposition (LMD) offers new perspectives for the fabrication of metal matrix nanocomposites (MMnCs). Current methods to produce MMnCs by LMD systematically involve the premixing of the nanopowders and the micropowders or require in-situ strategies, thereby restricting the possibilities to adjust the nature, content and location of the nano-reinforcement during printing. The objective of this study is to overcome such restrictions and propose a new process approach by direct injection of nanoparticles into a metallic matrix. Alumina (n-Al2O3) nanoparticles were introduced into a titanium matrix by using two different direct dry injection modes in order to locally increase the hardness. Energy dispersive X-ray spectroscopy (EDS) analyses validate the successful incorporation of the n-Al2O3 at chosen locations. Optical and high resolution transmission electron microscopic (HR-TEM) observations as well as X-ray diffraction (XRD) analyses indicate that n-Al2O3 powders are partly or totally dissolved into the Ti melted pool leading to the in-situ formation of a composite consisting of fine &alpha, 2 lamellar microstructure within a Ti matrix and a solid solution with oxygen. Mechanical tests show a significant increase in hardness with the increase of injected n-Al2O3 amount. A maximum of 620 HV was measured that is almost 4 times higher than the pure LMD-printed Ti structure.

The present study has investigated the influence of calcium process control agent on the microstructure and mechanical properties of powder metallurgy processed samples fabricated by milling and spark plasma sintering technique. The microstructure of spark plasma sintered Ti-6Al-4V with 0.3 wt% Ca (Ti-6Al-4V-0.3Ca-M) samples revealed fine grain structure compared to sintered unmilled (Ti-6Al-4V-UM) samples. The average grain size values of sintered Ti-6Al-4V-0.3Ca-M and Ti-6Al-4V-UM samples are 8 and 60 μm, respectively. The spark plasma sintered Ti-6Al-4V-UM exhibited a yield strength (YS) of 875 ± 10 MPa, ultimate tensile strength (UTS) of 1057 ± 2 MPa, and % elongation (% El) of 15 ± 2. The spark plasma sintered Ti-6Al-4V-0.3Ca-M exhibited higher YS of 964 ± 9 MPa, UTS of 1153 ± 7 MPa, and lower % El of 6 ± 1 when compared to mill annealed Ti-6Al-4V alloy (YS 899 MPa, UTS 978 MPa and %El 15). The higher strength of Ti-6Al-4V-0.3Ca-M sintered samples could be attributed to the fine grain structure and the presence of interstitial elements in the matrix. In contrast, the lower strength of Ti-6Al-4V-UM can be ascribed to its coarse grains.

Aluminium 6061 alloy matrix composite materials reinforced with carbon nanotubes (CNTs) and silicon carbide nanoparticles (nSiCs) were prepared by high-energy ball milling and hot pressing. In addition to inducing fine particle strengthening, nSiCs were also used as a solid mixing agent to improve the dispersion of the CNTs in the Al matrix powder. The dependence of the densification and mechanical strength of the composites reinforced with the dual nanoparticles on the milling time is discussed. The crystallite sizes of Al in the composites were also investigated. Moreover, the relative defect ratios of the CNTs in the composites were calculated from the intensities of the D and G peaks of the Raman spectra. With this new approach to composite fabrication, a hardness and tensile strength of 334 HV and 293 MPa, respectively, were achieved. The high-energy ball milling time significantly affected the microstructure and mechanical properties of the composites; however, the dual nanoparticle reinforcement can potentially be used in a variety of industrial component materials with precisely controlled material properties.

Microstructural and impression creep properties of hot pressed bulks made from unmilled AlMg5 powders, milled AlMg5, and AlMg5 powders milled with 0.5 vol% of Al2O3 nanoparticles are investigated. Microstructural, high-temperature impression creep, and high-temperature tensile properties investigation is carried out. Activation energies and stress exponent values are determined from the steady state creep rate obtained at different temperatures and creep stresses. AlMg5–0.5 vol% Al2O3 samples display superior strength values at 298 K compared to unmilled AlMg5 and milled AlMg5 samples. However, AlMg5–0.5 vol% Al2O3 nanocomposite exhibits higher creep rate and tensile elongation with a decrease in strength at 473 K due to activation of grain boundary sliding mechanism.

Spatter generated during laser irradiation of an aluminium alloy nanocomposite (AlMg5 reinforced with Al2O3 nanoparticles) was monitored by high speed imaging. Droplets trajectory and speed were assessed by computerized image analysis. The effects of laser peak power and laser focusing on the plume expansion and expulsed droplet speeds were studied in air or under argon flow. It was found that the velocity of visible droplets expulsed laterally or at the end of the plume emission from the metal surface was not dependent on the plasma plume speed. The neighbouring area of irradiation sites was studied by optical and scanning electron microscopy. Droplets deposited on the surface were classified according to their size and counted using a digital image processing software. It was observed that the number of droplets on surface was 1.5–3 times higher when the laser beam was focused in depth as compared to focused beams, even though the populations average diameter were comparable. Three methods were selected for removing droplets in situ, during plume expansion: an argon gas jet crossing the plasma plume, a fused silica plate collector transparent to the laser wavelength placed parallel to the irradiated surface and a mask placed onto the aluminium composite surface. The argon gas jet was efficient only for low power irradiation conditions, the fused silica plate failed in all tested conditions and the mask was successful for all irradiation regimes.

In the present study, powder metallurgy processed unmilled AlMg5 (AlMg5-UM), milled AlMg5 (AlMg5-M), and milled AlMg5–0.4 vol.% Al2O3 (AlMg5–0.4Al2O3) nanocomposite were successfully spark plasma sintered at 550 °C. The microstructural analysis of spark plasma sintered AlMg5-UM revealed equi-axed grains with average size of 20 ± 5 μm. The microstructural analysis of spark plasma sintered AlMg5-M and AlMg5–0.4Al2O3 revealed a bimodal grain structure with both fine-coarse grains of size 700 nm–8 μm and 300 nm–8 μm, respectively. The spark plasma sintered AlMg5-UM exhibited a yield strength (YS) of 132 ± 3 MPa, ultimate tensile strength (UTS) of 296 ± 2 MPa and % elongation (% El) of 22 ± 2 comparable to the conventional Al 5083 alloy — O temper (YS of 145 MPa, UTS of 281 MPa and % El of 16). The spark plasma sintered AlMg5-M and AlMg5–0.4Al2O3 exhibited YS of 242 ± 9 MPa and 274 ± 5 MPa, UTS of 376 ± 4 MPa and 417 ± 8 MPa and % El of 19 ± 1 and 10 ± 1, respectively. The lower strength (YS and UTS) of AlMg5-UM can be ascribed to its coarse grains. Among the milled samples, the AlMg5–0.4Al2O3 composite exhibited high strength and it can be ascribed to its fine grain size (Hall–Petch effect), higher dislocation density and Orowan strengthening effect due to Al2O3 reinforcements. Keywords: Spark plasma sintering, Nano-composites, Microstructure, Hardness, Mechanical properties

In the present study, powder metallurgy processed unmilled AlMg5, milled AlMg5 and milled AlMg5-0.5 vol% Al2O3 nanocomposite have been successfully friction stir welded (FSW). The effect of friction stir welding on the evolution of weld microstructures; hardness and tensile properties were studied and discussed in detail. FSW of unmilled AlMg5 resulted in significant grain refinement and strain hardening in the nugget zone induced by the thermo-mechanical processing, thereby increasing the stir zone hardness and tensile strengths to 100 HV and 324 MPa when compared to 80 HV and 300 MPa of base metal, respectively. In contrast, the FSW of milled AlMg5 and milled AlMg5-0.5 vol% Al2O3 samples showed a reduction in UTS values to 375 MPa and 401 MPa in the stir zone compared to 401 MPa and 483 MPa of respective base metal values. Transmission electron microscopic (TEM) investigation of weld stir zones revealed the homogenous distribution of Al4C3 nanophases in milled AlMg5 and Al2O3 nanoparticles in milled AlMg5-0.5 vol% Al2O3 samples throughout the aluminium matrix. It was revealed that the pre-stored energy from the prior ball milling and hot pressing processes, higher deformation energy and grain boundary pinning effect due to the presence of reinforcement particles has resulted in a higher recrystallization tendency and retarded grain growth during FSW of milled samples. The welds prepared with milled AlMg5-0.5 vol% Al2O3 exhibited higher hardness and tensile strength in the stir zone when compared to all other conditions which was attributed to Hall Petch effect due to fine grain size and Orowan strengthening effect due to Al2O3 reinforcements.

The effect of interaction of lasers having different spectral and temporal profiles with titanium on the weld surface quality is investigated by high-speed imaging and optical emission spectroscopy at atmospheric pressure in argon environment. High-speed imaging of the plume reveals that plume is produced during the laser pulse. Decrease in plume size and expansion rate is observed for those lasers whose spectral profiles overlap with more number of neutral atomic titanium transitions (Ti I) owing to increasing rate of reabsorption of the laser pulse primarily by the neutral titanium atoms present in the plume. Darkness around the laser spot on the titanium surface observed due to deposition of the nanoparticles increases with decrease in size and expansion rate of the plume which indicates that reabsorption of the laser pulse is the main cause of dark colouration of the surface. The bright appearance of a part of the plume produced by one laser at which another laser whose spectral profile cover many Ti I transitions is passed confirms the reabsorption process. Clean appearance of the surface around the laser spot along with enhancement of the plume size and expansion rate is observed for lasers with customized spectral profiles which do not overlap with any Ti I transitions. Modulation of the temporal profile can moderately improve the plume expansion rate and reduce the darkness around the laser spot provided that the laser spectral profile does not overlap with many Ti I transitions, particularly, with those whose energy of lower levels is less than 3 eV.

International audience; Titanium carbonitride nanoparticles have been produced in an inductively coupled thermal plasma and subsequently modified using a surfactant that has been deposited in situ on their surface in-flight. The surfactant was injected in the reactor while the nanoparticles are still dispersed in the gas phase, allowing the coating of primary particles instead of the corresponding agglomerates. In contrast to naked TiCN nanoparticles, the surfactant coated particles could be readily dispersed in water with a short ultrasonic treatment and built up no large agglomerates as proved by Photon Correlation Spectroscopy measurements. The investigated surfactants seem, however, to undergo a chemical modification and/or a thermal degradation at the surface of the TiCN nanoparticles.

AlMg5-based metal matrix composites were successfully fabricated using high energy planetary ball-milling and hot pressing. The influence of 6 types of carbon nanotubes (CNTs) with different properties was investigated for reinforcement. Over 3 fold increase in hardness and ultimate tensile strength was achieved with maximum values of 200 HV 20 and 720 MPa respectively by varying CNT content from 0.5 to 5 vol%. The state, the dispersion as well as the reactivity of the different CNTs were investigated by Raman spectroscopy, X-Ray diffraction and microscopy. The CNTs were considered to be dispersed homogeneously, but were shortened due to high energy milling. No significant differences in mechanical performances could be observed depending either on the nature or on the agglomeration initial state of the investigated CNTs. The milling time has to be however adjusted to the CNT content as higher concentrations require a longer milling time for achieving dispersion of the nano-reinforcement.

There is a continuous demand for next-generation industrial materials because they offer advantages such as high performance, reliable life cycle, reasonable cost, and ease of mass production. Carbon nanotubes (CNTs), which possess unique properties such as beneficial mechanical, electrical, and thermal properties, as well as chemical stability, have received considerable attention as candidates for reinforcing ultra-high-performance nanocomposites. CNT-reinforced Al alloy matrix nanocomposites were fabricated by mechanical ball-milling and hot-pressing processes. The effects of different CNTs on the mechanical properties of the composites were investigated. The mechanical properties were found to change significantly depending on the type of CNT blended with the matrices. The mechanical performance of the nanocomposites can thus be controlled by using different types of CNT reinforcements.

Nanodiamond (nD) and multi-walled carbon nanotubes (CNT) was used to fabricate reinforced pure aluminum (Al) matrix composites by mechanical ball milling and hot-pressing. Pure Al bulk and each single nanoparticle (nD or CNT) reinforced composites was also fabricated for comparison. Micro-Vickers hardness was measured for single (nD or CNT) and dual nanoparticle (mixture of nD and CNT)-reinforced Al matrix composites and showed maximum values that were approximately six times higher than those of pure Al bulk. Four-point bending behaviors were also discussed and the dual nanoparticles-reinforced Al matrix composites showed highest value of the flexural strength (about 760 MPa). The fracture surfaces that resulted from the bending test were also observed. Moreover, the crystallite size and lattice strain of the Al particles in the composites were described by the Scherrer equation.

Currently, Additive Manufacturing (AM) is limited to three classes of materials: ceramics, polymers and metals. Even within these classes, only a small number of materials can be processed by AM, either in a powder bed approach or in a direct energy deposition approach.

Functionally graded (FG) carbon nanotubes (CNT) and nano-silicon carbide (nSiC) reinforced aluminium (Al) matrix composites have been successfully fabricated using high-energy ball milling followed by solid-state spark plasma sintering processes. The CNTs were well-dispersed in the Al particles using the nSiC as a solid mixing agent. Two different types of multi-walled CNTs were used to add different amounts of CNTs in the same volume. The ball milled Al–CNT–nSiC and Al–CNT powder mixtures were fully densified and demonstrated good adhesion with no serious microcracks and pores within an FG multilayer composite. Each layer contained different amounts of the CNTs, and the nSiC additions showed different microstructures and hardness. It is possible to control the characteristics of the FG multilayer composite through the efficient design of an Al–CNT–nSiC gradient layer. This concept offers a feasible approach for fabricating the dual-nanoparticulate-reinforced Al matrix nanocomposites and can be applied to other scenarios such as polymer and ceramic systems.

The macro hardness (HV 20 ) was measured for aluminium and 1–9 wt% Multi Wall Carbon Nanotubes (MW-CNTs) composites that were milled and hot compressed. The hardness increased with increasing fraction of MW-CNTs up to 6 wt% (HV 20 = 151) and then remained constant. The content of MW-CNTs was significantly higher than reported for similar materials and measurements. The composites were analysed by Raman, TEM and XRD. The Raman and TEM showed MW-CNTs were still present after milling and hot pressing. The XRD was used to determine the Al crystallite size which was used to determine Hall–Petch contribution to the composite hardness.

Carbon nanotubes (CNT) and nano-silicon carbide (nSiC)-reinforced aluminum (Al)-6061 alloy matrix composite materials were fabricated using high-energy ball milling and hot-pressing processes. The nSiC was used not only as a solid mixing agent to better disperse the CNTs in the Al powder, but also as a mean of inducing fine particle strengthening. The densification behavior of the dual-nanoparticulate-reinforced composites varied with the milling time. The crystallite sizes of Al in composites became significantly smaller when the milling time was increased. Moreover, the high-energy ball milling time significantly affected the microstructure and mechanical properties of the composites. We believe that the dual-nanoparticulate-reinforced composites can be used in a variety of applications as industrial component materials with precisely controlled properties.

This research describes an investigation of the interfacial phases formed between aluminum (Al) and carbon nanotubes (CNT) which properties depend on the processing temperature (below, slightly above and over the melting point of Al). Al–CNT compacts were prepared by spark plasma sintering followed by heat treatment in order to observe the interface phases. The microstructures of both the as-sintered and heat-treated materials have been observed by optical, scanning and transmission electron microscopies. The amorphous Al oxide observed at the boundaries in the as-sintered material is transformed to crystalline Al oxide after the heat treatment. In addition, some of the CNTs decomposed and reacted with the Al, resulting in the formation of Al carbide which shows different size distributions depending on the heat treatment temperature. According to the results, it is possible to control the phase formed at the Al–CNT interface by controlling the process temperature and those controlled interfaces will be playing important role to the properties in a bulk materials.

The role of hydrogen and methane dissociation process in induction plasma synthesis of graphene nano-flakes (GNF) is studied by the optical emission spectroscopy of Ar/H2/CH4 plasma. The condensation of C2 species formed due to methane decomposition produces GNF, which depends on pressure. Electron impact and dehydrogenation processes dissociate methane, which promotes and hinders the GNF production, respectively. The effect of hydrogen is insignificant on quality, size and morphology of the GNF. The CH4 flow rate has no influence on particle temperature but has effect on cooling rate at the point of nucleation and, therefore, on production rate and thickness of GNF.

Aluminium 6061 has proven to be a suitable alloy as a basis for producing metal matrix composites (MMC). These MMCs have a low specific weight combined with a relatively good specific stiffness and high specific strength. The hardness and compressive strength of Al composites can be increased by reinforcing bulk material with nano particles. However the ductility of such alloys is relatively low, therefore one of the applications for such light alloys could be wear applications. In many wear conditions such as erosive or abrasive wear at normal impact angles the surface wear resistance plays a significant role. The surface fatigue properties have not been widely studied for such nanoparticle reinforced aluminium composites. The nano-reinforced composite materials were produced by means of high-energy milling (HEM) of nano-sized reinforcement particles together with a metallic matrix powder, followed by hot pressing. By utilizing up to 6 wt% multiwalled carbon nanotubes (MWCNT) as reinforcement the hardness of Al6061 MMC has been increased from 45 HV10 up to 317 HV10, compressive yield strength from 58 MPa up to 660 MPa and indentation modulus from 60 GPa up to 90 GPa compared to hot pressed Al6061. Surface fatigue tests were conducted at impact (dynamic) loading conditions using a hardened steel sphere as indenter. The Wöhler-like curves are plotted to estimate the surface fatigue. The surface fatigue indents were photographed by the aid of light optical microscopy (LOM) and analysed by image analysis software and optical profilometry (OP).

International audience; We have successfully fabricated highly densified aluminum (Al)-diamond composite materials by a simple hot press method. The thermal conductivity of the Al-diamond composite materials was measured. These materials had different types, sizes and fractions of diamond. These obtained values were discussed based on theoretically calculated values. The thermal conductivity of the composite materials, measured by Laser-Flash method, was found to have slightly increased compared to that of pure bulk Al. The obtained microstructures of the composite materials showed a lot of cleavage existing in the interface between the Al matrix and the diamond particles, which led to the low increment of the thermal conductivity. Moreover, Al-diamond bulk materials with different sintering temperatures in solid state, liquid phase, and transient region between solid and liquid of Al, have been synthesized.

High-energy milling was studied for the ex situ strengthening of aluminium with silicon carbide (SiC) nanopowders. Heptane was used as a milling agent for both planetary- and attritor ball milling. Considering the different milling techniques and the differences in the resulting powders, effective dispersion of the nano SiC was achieved. Composite samples compacted by hot pressing showed an increase in hardness (HV 20 = 220) and a decrease in Al crystallite size from 220 to 55 nm with the nano-SiC content increasing from 1 up to 20 vol.%. The ultimate tensile strength was measured for extruded samples which resulted in 205 MPa (17% elongation) for 1 vol.% of nano-SiC and a strength of 420 MPa (4% elongation) for 10 vol.% of nano-SiC reinforcement. The mechanical properties were compared with what was predicted by the Hall–Petch relationship.

Spark plasma sintering and hot extrusion processes have been employed for fabricating carbon nanofiber (CNF)-aluminum (Al) matrix bulk materials. The Al powder and the CNFs were mixed in a mixing medium of natural rubber. The CNFs were well dispersed onto the Al particles. After removal of the natural rubber, the Al-CNF mixture powders were highly densified. From the microstructural viewpoint, the composite materials were observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. The CNFs were found to be located on every grain boundary and aligned with the extrusion direction of the Al-CNF bulk materials. Some Al carbides (Al4C3) were also observed at the surface of the CNFs. This carbide was created by a reaction between the Al and the disordered CNF. The CNFs and the formation of Al4C3 play an important role in the enhancement of the mechanical properties of the Al-CNF bulk material. The CNFs can also be used for engineering reinforcement of other matrix materials such as ceramics, polymers and more complex matrices.

Functionally graded carbon nanotube (CNT)-reinforced aluminum (Al) matrix composites have been successfully fabricated by a powder metallurgy route. The gradient layers containing different amounts of CNT additions showed different microstructures and hardness. Each layer demonstrated good adhesion, with no serious pores or microcracks. We controlled the characteristics of the bulk composite by the efficient design of each CNT gradient layer. The functionally graded material concept offers a feasible approach to fabricating Al-CNT nanocomposites.

High-energy planetary milling was used for mixing aluminium powders with 1 vol.% of silicon carbide (SiC) nanoparticles. A number of milling parameters were modified for constituting the relationship between the energy input from the balls and the hardness of the bulk nanocomposite materials. It was shown that mixing characteristics and reaction kinetics with stearic acid as process control agent can be estimated by normalised input energy from the milling bodies. For this, the additional parameter characterising the vial filling was determined experimentally. Depending on the ball size, a local minimum in filling parameter was found, laying at 25 or 42% filling of the vial volume for the balls with diameter of 10 and 20 mm, respectively. These regions should be avoided to achieve the highest milling efficiency.After a hot compaction, fourfold difference of hardness for different milling conditions was detected. Therewith the hardness of the Al–1 vol.% nanoSiC composite could be increased from 47 HV 0.5 of pure aluminium to 163 HV 0.5 when milling at the highest input energy levels.

Titanium carbonitride nanoparticles produced from the inductively coupled plasma process were investigated by high resolution analyses such as transmission electronic microscopy and energy electron loss spectroscopy. TiCN nanopowders with grain sizes below 30 nm were obtained. The control of the plasma chemistry and the residence time of the precursors in a temperature above the boiling point of TiCN lead to either stoichiometric, or C-rich or also N-rich nanopowders. A surface oxidation takes place when the nanoparticles are brought to air for ex situ characterizations after thermal plasma processing.

The synthesis of silicon nanopowders by an inductively coupled plasma (ICP) process is investigated. The specific surface area (SSA) of the elaborated particles is determined by nitrogen absorption (BET) as a function of the quenching gas flow rate and the precursor feeding rate. Nanopowders with specific surface areas varying from 69 to 194 m2 g− 1, corresponding to equivalent particle sizes of 37 and 13 nm respectively, could be produced. The correlation between these two input parameters and the output SSA has been numerically modelled with linear regression and artificial neural networks approaches. It has been demonstrated that with the available data set, a regression model with quadratic regressors and a neural network modelling give a similar response.

In the growing field of nanomaterials, SiC nanoparticles arouse interest for numerous applications. The inductively coupled plasma (ICP) technique allows obtaining large amount of SiC nanopowders from cheap coarse SiC powders. In this paper, the effects on the SiC structure of the process pressure, the plasma gas composition, and the precursor nature are addressed. The powders were characterized by X-ray diffraction (XRD), Raman and fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and high resolution electron microscopy (HREM), chemical analyses, BET and photon correlation spectroscopy (PCS) measurements. Whatever the precursor (α- or β-SiC), the nanoparticles were crystallised in the cubic β-SiC phase, with average sizes in the 20-40 nm range. Few residual grains of precursor were observed, and the decarburization due to the reductive Ar-H2 plasma lead to the appearance of Si nanograins. The stoichiometry of the final product was found to be controllable by the process pressure and the addition of methane.

Nanoparticles show novel properties compared to the bulk material of same chemistry. The small size is responsible for many changes in the thermo-physical properties. Thus, there was an increasing interest in nanomaterials since the past five years. Among other methods, inductively coupled plasma (ICP) torches can be used for the synthesis of nanoparticles. In this process, the precursor material is vaporized in a first step in the plasma core. In a second step, nucleation and condensation occur in the synthesis chamber where the plasma gets colder and form high-purity nanoparticles, the growth of which is stopped by gas quenching. From their low velocity and high temperature, induction plasmas are particularly adapted for this application. Numerical modeling is a good way to achieve a better knowledge and understanding of the process. In the present paper, a two-dimensional model of an inductively coupled plasma torch was developed and validated on the basis of comparisons with data obtained by some other authors. Finally, the current frequency (13.56 MHz), pressure level (400 mbar) and gas flow rates were adjusted for the specific conditions of nanoparticles synthesis.

This paper presents a short overview of the high flexibility and potential of inductively coupled thermal plasmas for the synthesis of nanoparticles and especially high refractory carbide nano-powders. The high energy and temperature of theses plasmas enable the evaporation of all materials allowing the use of solid precursors that are cheap and commercially available. By controlling the temperature history of each particle, the growth mechanisms can be stopped at the requested particle size. Therefore in-situ monitoring and process modelling are proved to be powerful tools.

An experimental study has been performed to gain some insight into the correlations between the deposition conditions and the structure of boron nitride (BN) coatings that are used in ceramic-matrix composites. BN has been deposited at 700°C from BCl 3 -NH 3 -H 2 mixtures on various substrates, by using chemical vapor deposition (CVD) and isothermal-isobaric chemical vapor infiltration (ICVI) processes, simultaneously in the same reactor. A kinetic study has shown that the CVD process is governed either by a combination of mass transfer with chemical kinetics at low flow rates or by the heterogeneous kinetics only at high flow velocities. In contrast, the limiting contribution of mass transfer always is observed for the ICVI process. The influence of diffusion cages that are positioned around the fibrous preforms is reported. The structure of BN deposits has been studied as a function of the various deposition conditions via transmission electron microscopy. The chosen CVD conditions lead to a poor organization of the BN deposits. Fairly well-organized BN coatings are deposited on all fibers of a fibrous preform via ICVI. The results are discussed in terms of supersaturation and deposition yields. The use of diffusion cages and the adjustment of the inlet composition and mass flow rate seem to be very important to obtain the best BN organization and thickness uniformity.

The present study investigated the influence of heptane and tin process control agents on cube milled Ti–6Al–4V + 0.5 Vol% TiC (Ti–6Al–4V–0.5TiC) powder. A smaller particle size and nar-row particle distribution was observed for Ti–6Al–4V–0.5TiC powder milled with heptane, while the powder milled with tin showed relatively larger particle size and broader particle distribution due to the cold welding of particles. Hcp phase was observed in the Ti–6Al–4V–0.5TiC powder milled with tin. The formation of fcc Ti(C, H)metastable phase with high lattice strain and interstitial content in Ti–6Al–4V–0.5TiC powder milled with heptane, resulted in higher hardness compared to the powder milled with tin.

Journal of Nanoparticle Research, 15, ISSN:1388-0764, ISSN:1572-896X

Carbon nanotube (CNT) reinforced aluminum (Al) matrix composite materials were successfully fabricated by mechanical ball milling followed by powder hot extrusion processes. Microstructural analysis revealed that the CNTs were well dispersed at the boundaries and were aligned with the extrusion direction in the composites obtained. Although only a small quantity of CNTs were added to the composite (1 vol%), the Vickers hardness and the tensile strength were significantly enhanced, with an up to three-fold increase relative to that of pure Al. From the fractography of the extruded Al–CNT composite, several shapes were observed in the fracture surface, and this unique morphology is discussed based on the strengthening mechanism. The damage in the CNTs was investigated with Raman spectroscopy. However, the Al–CNT composite materials were not only strengthened by the addition of CNTs but also enhanced by several synergistic effects. The nanoindentation stress–strain curve was successfully constructed by setting the effective zero-load and zero-displacement points and was compared with the tensile stress–strain curve. The yield strengths of the Al–CNT composites from the nanoindentation and tensile tests were compared and discussed. We believe that the yield strength can be predicted using a simple nanoindentation stress/strain curve and that this method will be useful for materials that are difficult to machine, such as complex ceramics.

Summary form only given. Silicon nanopowders have been synthesized from micrometric Si precursors using lab-scale radio-frequency induction thermal plasma (RF-ITP) system. The latter is composed of a commercial inductively coupled plasma torch (Tekna PL-35) mounted on a reaction chamber characterized by a cylindrical geometry [1, 2] under soft vacuum. Nanopowder samples have been collected at different positions in the reaction chamber and in the filter at the outlet of the reactor and successively characterized using a particle size analyzer and BET analysis. The influence of processing parameters of the RF-ITP system (power level, pressure and powder feed rate) on size distribution and surface area of the synthesized nanopowders has been investigated.